1. Field of the Invention
The present invention relates to capacitors formed on conductive surfaces, preferably silicon surfaces, during the construction of integrated circuits. More specifically, the present invention relates to a method of making a capacitor in which silicon nitride barriers are formed between conductive surfaces forming the plates of a capacitor and a capacitor dielectric layer of tantalum oxide located between the conductive surfaces.
2. Description of Related Art
As the memory size of dynamic random access memory (DRAM) devices increases into the gigabit range, the dimensions of all memory structures and the space allotted on the semiconductor substrate for those structures have decreased. To produce capacitors of the necessary value within the limited space available, conventional oxide/nitride/oxide stack dielectrics have had to be constructed ever thinner and thinner. Such stack dielectrics are beginning to reach the practical limit of how thin they may be deposited.
One solution to this is to use tantalum oxide to replace oxide/nitride/oxide stacks as the capacitor dielectric. Tantalum oxide (Ta.sub.2 O.sub.5) has a higher dielectric constant and produces a correspondingly higher capacitance in the resulting capacitor.
A problem with the use of tantalum oxide, however, is that the tantalum oxide deposition process results in the formation of a thin silicon oxide interface when the tantalum oxide is deposited directly on a polysilicon bottom electrode.
This silicon oxide interface reduces the overall capacitance and degrades device functionality. To prevent the formation of the undesirable silicon oxide interface, it is known to deposit a thin nitride layer over the polysilicon before depositing the tantalum oxide. This nitride layer has a higher dielectric constant (K.sub.SiN =7) than the silicon oxide (K.sub.SiO2 =4).
In the prior art implementation of this deposition process, the nitride layer has been deposited using a rapid thermal nitridation (RTN) process. The RTN process, however, is a relatively slow and costly process. This results from the multiple processing steps required. Further, the RTN process results in a nitride layer that is not uniformly thick. This adversely affects the performance of the capacitor being constructed.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of making a capacitor in which the capacitor dielectric layer is separated from the conductive surface by a silicon nitride layer that is uniformly thick.
It is another object of the present invention to provide a method of making a capacitor in which the capacitor dielectric layer is separated from the conductive surface by a silicon nitride layer that can be constructed with fewer steps and less expensively than when constructed with the RTN process.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.